Accurate adjustment of a clearance between internal combustion engine intake, exhaust, and other valves is important if maximum engine performance and economy are to be obtained. This clearance may also be referred to as “valve lash”. Measuring, adjusting and controlling of valve lash is important to take into account the inherent tolerances and variations in the initial manufacture and assembly of the many mechanical engine components and throughout the life of the engine. Failure to accurately measure valve lash and make necessary adjustments thereto may result in gradual degradation of engine performance and reduced fuel combustion efficiency. Engine manufacturers typically have specific requirements for setting valve lash. For example, an engine manufacturer may specify that an intake valve lash should be set to 0.3 to 0.5 mm, that an exhaust valve be set to 0.6 to 0.8 mm, or that a Jake Brake valve be set to 0.8 to 1.2 mm.
In prior processes, valve lash may be initially set by a worker manually screwing in or backing out an adjuster screw that contacts the spring structure that moves a valve. The worker would manually tighten or loosen the adjuster screw while measuring the valve lash using, for example, feeler gauges. After the worker has manually adjusted the adjuster screw such that the valve lash is within the manufacturer's specified range, the worker must hold the adjuster screw stationary while tightening a lock nut. This process can be problematic for various reasons. For example, measurements taken with feeler gauges are often inaccurate due to inconsistent feeler gauge use from measurement to measurement, especially between different workers. As another example, if the adjuster screw is inadvertently allowed to move while tightening the lock nut, the lash setting can change defeating the principal objective of the process.
As an alternative to manually measuring valve lash, valve lash can be set by a processes using an automated tool. For example, in one such process, an adjuster screw torque at which a valve is set to a zero lash position can be determined experimentally by performing repeated measurements of one or more test engines of a certain type. Then, when setting the valve lash on an engine of the same type, the valve lash can be initially set such that the experimentally determined adjuster screw torque is achieved, and the valve can be assumed to be set at the zero lash position at the experimentally determined torque. From the zero lash position, the adjuster screw can be turned a known amount based on a pitch of the adjuster screw in order to obtain the specified valve lash setting.
These prior processes although useful, were imprecise, time and labor intensive and only slightly improved on reducing or minimizing the many variations and tolerance stack-ups inherent in the complex mechanical engine system. These prior lash setting processes relied on empirically derived averages to estimate a zero crossing point or zero lash point of a particular valve assembly which is a necessary starting point to set a predetermined or specified lash distance or setting for optimal operation of the valve system and overall engine performance. The prior processes did not measure or take into account the many mechanical variations and tolerances present in different engines of the same type much less the mechanical variations that occur between individual valve assemblies in a single engine.
Thus there is need for a process that improves on the many shortcomings and disadvantages of prior valve lash setting processes which is fast enough for high volume production facilities, is economic, easy to implement and use, and is repeatable.